Ladder Switch Circuit for High-Voltage Battery Cell Balancing
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Solution Overview
Problem
Existing battery systems face challenges in balancing the voltage of storage units, particularly at higher voltages like 400V, which is not optimal for system powers of several 100 kW, and existing balancing methods are either inefficient or costly, especially when scaling beyond individual battery modules.
Innovation Solution
A circuit and method for balancing the voltage of storage units, utilizing a ladder-like network of switches and a balancing source to adjust the voltages of multiple units in series, allowing for scalable voltage balancing across a series connection of storage units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive balancing with resistors is used, then the circuit complexity is low, but the balancing process takes several days and productivity is very low
Solution Approach 1:
The patent replaces passive resistor-based balancing with an active electronic switching system using MOSFETs and control circuits. This substitution enables rapid voltage equalization by actively transferring charge between cells through electronic switches, rather than relying on slow passive resistor discharge, thereby dramatically improving balancing speed while maintaining manageable circuit complexity through integrated control.
2Productivity
If active balancing with clocked circuits is used, then balancing speed improves, but cost and device complexity increase significantly
Solution Approach 1:
The patent merges the balancing function with the existing battery management system structure. The control unit integrates multiple functions (voltage monitoring, switch control, charge management) into a single coordinated system. By combining these functions and using a unified control architecture with MOSFETs that can operate in multiple modes, the patent achieves fast active balancing while reducing overall system complexity compared to separate dedicated balancing circuits.
Solution Approach 2:
The control unit and MOSFET switches serve multiple functions: they enable fast balancing by transferring charge between cells, provide overcharge protection, facilitate cell equalization during charging, and can operate in different configurations (series/parallel). This multi-functionality reduces the need for separate dedicated circuits, thereby improving balancing speed without proportionally increasing complexity.
3Power
If battery modules operate at 400V, then system power capability increases, but voltage balancing becomes more difficult and reliability decreases
Solution Approach 1:
The patent segments the high-voltage battery system into individually controllable modules or cells, each with its own monitoring and switching capability. The control unit can selectively activate specific MOSFETs to balance voltage between individual cells or groups of cells, even at 400V operating levels. This segmentation enables precise voltage management across multiple series-connected units, maintaining reliability while achieving high system power capability.
Data Source
AI summary
A circuit, a method and a system are provided for balancing the voltage of storage unit connected in series. The circuit corresponds to a ladder network in which horizontal switches form the rungs of the ladder, a storage unit is respectively arranged on the first rail of the ladder between the rungs and a vertical switch is respectively arranged on the second rail between the rungs. By switching the horizontal switches and vertical switches, respective storage units can be connected to a balancing source so that the latter adjusts the voltage of the connected storage unit, whereby the voltage of the storage units in the series connection is balanced.